Control Your Linux Desktop with D-Bus

If you want to do more complex tasks than calling a single method, you
can write a shell script with dbus-send commands or use a
higher-level language to simplify the task.
There are D-Bus bindings for languages such as Python, Ruby and Java.

In this next example, I implement a Python script that
sets your status on Pidgin to “Away from keyboard” if your screensaver
activates. This shows two aspects of D-Bus: the script waits for a signal
from the screensaver, and then it calls a method in Pidgin. The script
is shown in Listing 1.

Let's dissect this script. The function pidgin_status_func sets your
status in Pidgin. It gets the im/pidgin/purple/PurpleObject object and
then the im.pidgin.purple.PurpleInterface interface from the session
bus. Then, it calls this interface's methods. It creates a new “saved
status” type by first checking if the status type with name
“afk” exists,
and if not, it creates it (“afk” stands for “Away From
Keyboard”,
and 5 is the “away” status type).

Then, the function checks the state variable that is an argument to
the pidgin_status_func function call (I explain what this argument
means later). If the argument is true, it sets the status message of the
new “afk”
status to “Away from keyboard” and activates the new status.
The effect is that Pidgin shows your status as “afk” with the
status message “Away from keyboard”.

Now you need to call this function when the screensaver
activates. Therefore, start the dbus main loop and connect to the
session bus. Then, add a signal receiver that listens to the signal
ActiveChanged from the org.gnome.ScreenSaver interface. If/when the signal
fires, it calls out pidgin_status_func function. As the
ActiveChanged signal has a boolean argument that signifies the current
state of the screensaver (1 for active and 0 for non-active), you have
defined one argument called state in the pidgin_status_func function.
To keep listening, let the loop run indefinitely, as long as the script
is running.

Pidgin has an extremely rich D-Bus interface;
you can do almost anything with it. So let this example give you some
inspiration to do some creative tasks in Pidgin!

Playing D-Bus

Let's look at another example, this time in Ruby. We're going to create
a script that shows the currently playing song in Rhythmbox as your
status in Pidgin (Listing 2).

Here you see the same type of commands as I used in the Python script:
open a D-Bus session, define D-Bus services, objects and interfaces,
and I define a signal receiver. And, a loop runs indefinitely to keep
listening to the D-Bus signals.

Of course, this could be tidied up a bit.
For example, you now are showing only the file path of the song as the status
message. I'll leave it to the reader to extract the relevant ID3 tags out
of the file and show them instead of the file path.